System for detecting small openings in hollow bodies

ABSTRACT

Light source and light sensor on opposite sides of wall of container detect pinhole or crack in container wall, with container rejection means operable by light sensor.

BACKGROUND OF THE INVENTION

Hollow bodies of containers or the like, and particularly can bodieshaving one closed end, may require testing to eliminate the possibilityof any small opening through any wall of the container being tested, inorder to avoid subsequent leakage of liquids or gases packed underpressure in the container. A conventional means for such testing is aBorden Tester, which operates on the basis of detecting air leakagethrough the walls of the container after maintaining a predeterminedpressure difference between air inside and outside the container over apredetermined period of time. Such pressure differential tests systemsare less sensitive than desired, and also require longer testing timethan is desirable for high speed production line purposes. Accordingly,a more sensitive and faster system of detecting potential leakers hasbeen wanted in the can manufacturing industry.

SUMMARY

The invention provides improved sensitivity and shorter testing times byproviding a light source and a light detecting means, so positionedrelative to a container that any opening through the container walltransmit light through the wall from the light source, which is detectedon the other side of the wall by the light detector. The detector ispreferably mounted to collect light inside the container, while thelight source directs light all around the outside of the container.

Other details and advantages of the invention will become apparent asthe following description of the embodiment thereof in the accompanyingdrawing proceeds.

DESCRIPTION OF THE DRAWING

The accompanying drawing shows schematically an embodiment of theinvention, in which

FIG. 1 is a side elevation of apparatus embodying the invention; and

FIG. 2 is a plan elevation of the apparatus shown in FIG. 1.

DESCRIPTION OF ILLUSTRATED EMBODIMENT

Referring now more particularly to the drawing, there is shown a can 10having a closed end 12, and an open end 14 terminating in a rim 16. Therim 16 rests on a conical support 18, and a bar 20 presses down on theend 12 to wedge the rim 16 against the support 18, thereby tending toopen up any incipient crack in the rim 16.

The support 18 constitutes the upper part of a hollow shield member 22within which there is mounted a light sensing element 24. A centralaperture 26 through the support 18 forms an opening concentric with thecan 10 and of less diameter than the internal diameter of the rim 14,for purposes of exposing the light sensor 24 to any light entering theinterior of can 19, either directly or after reflection from theinterior surfaces of the can. It is thus desirable that these internalsurfaces be relatively bright.

A plurality of lights 28 are mounted above and around the outside of thecan 10, augmented by any reflectors which may be helpful (not shown), inorder to pass light through any openings which may occur in the form ofpinholes, cracks, or the like in the source of the can 10. The lightsensor 24 is connected to suitable electronic means 30 connected in turnto means 32 for moving the can 10 in one direction if no light isdetected by sensor 24, and also to means 34 for moving the can 10 in adifferent direction if light is detected by sensor 24. Such electroniccontrols and acceptance and rejection means can take various forms wellknown to those skilled in the art. For purposes of schematicillustration, the means 32 and 34 can take the form of pneumatic ormechanical or other means for acting on the can 10 to move it indifferent directions, as more particularly shown in FIG. 2. However, forplant purposes several cans may be tested at once at adjacent stations,and the controls must include known delay means for rejecting defectivecans after they have moved down the line after testing.

The hold-down bar 20 is preferably of transparent material, so that itwill not block passage of light into can 10 while the bar 20 is incontact with the can 10. However, it may be desirable to improvesensitivity of detection by passing the can 10 through successivetesting stations in which the hold-down bar is oriented in differentdirections so that the whole exterior surface of the can is necessarilyexposed to light in the course of such successive tests.

The light sensing element 24 is preferably extremely sensitive to evensmall amounts of light, and consequently should be protected againstexposure to the lights 28 during periods when the can 10 is not over theaperture 26. Such protection can be achieved by turning on lights 28only while the can 10 is in place, or else, for example, by installingsuitable shutters over the aperture 26, for purposes of opening theaperture 26 when each test begins and closing it as soon as each test iscompleted.

The system of the invention is particularly well adapted to bright metalcans, e.g., drawn and ironed aluminum cans. However, it is obvious thatthe shape and material and surface of the can can be varied withoutprecluding application of the system of the invention to such a can.

As used herein, the term "light" refers to rays detectible by the humaneye or by other means.

I claim:
 1. Apparatus for testing for any random perforation in thewalls of container bodies having brightly reflective interior surfaces,comprising means to make light-tight engagement with the end of the wallat the open end of a container body, means to sense light passed fromwithin the container body to said open end, and light source means toilluminate the outside of the container body walls to be tested, wherebylight from said light source means can pass through any randomperforation in said walls to be tested, and thence enter the interior ofthe container to pass directly or by reflection from .Iadd.the brightlyreflective interior surfaces .Iaddend.within the container body.Iadd.directly .Iaddend.to the light sensing means, thus indicatingwhether the container body is perforated.
 2. Apparatus .[.according toclaim 1,.]. .Iadd.for testing for any random perforation in the walls ofcontainer bodies having brightly reflective interior surfaces,comprising means to make light-tight engagement with the end of the wallat the open end of a container body, means to sense light passed fromwithin the container body to said open end, and light source means toilluminate the outside of the container body walls to be tested, wherebylight from said light source means can pass through any randomperforation in said walls to be tested, and thence enter the interior ofthe container to pass directly or by reflection from within thecontainer body to the light sensing means, thus indicating whether thecontainer body is perforated, and further .Iaddend.including means topress the container body against said .[.member.]. .Iadd.first means.Iaddend.and thereby tend to open up any edge crack at the open end ofthe container body, whereby light from the light source means will tendto pass through the edge crack to be detected by the light sensingmeans.
 3. Apparatus according to claim 2, in which said light sensingmeans has its light sensitive element positioned entirely outside of theinterior of the container body and in which an open passage is providedfor transmission of light passing from the interior of the containerbody to the light sensitive element.
 4. A method for testing the sidewalls and bottom of an open ended metal container having brightlyreflective interior surfaces, which comprises the steps of interposing alight barrier between the interior and exterior surfaces of thecontainer, pressing a portion of the barrier against the end of the sidewalls at the open end of the container exposing the exterior surfaces ofthe container to light rays, and sensing light passing .Iadd.directly orby reflection from the brightly reflective interior surfaces within thecontainer directly .Iaddend.toward the open end of the .[.can.]..Iadd.container .Iaddend.from its interior, thereby detecting any lightpassing from outside the container through any random perforationthrough its walls into the interior of the container.